The present invention relates generally to a droop compensated regulator used to regulate the input to transistor-based loads, such as RF preamplifiers and amplifiers employed for driving solid state pulsed radar transmitters.
Voltage regulators are used in a variety of contexts for providing and regulating the voltage applied to electronic circuit devices. Just by way of example, voltage regulators are an important system component in solid state pulsed radar systems. In that context, voltage regulators are used to regulate the voltage supplied to various loads such as preamplifiers or amplifiers that power the radar transmitter circuitry.
One common problem with linear voltage regulators is that their voltage output will tend to decrease during loading (e.g., during transmit gate pulses) until the regulator senses the error and begins to regulate the output voltage. This decrease is sometimes referred to as the output voltage xe2x80x9cdroop.xe2x80x9d Generally, this problem is attributable to the voltage regulator output capacitance where the voltage across the capacitor decreases or droops (dV=1/C*Idt). In the context of a pulsed radar system, this droop in the output voltage causes a decrease in the RF transistor power output. This results in suboptimal system performance.
This problem of a decrease in the RF transistor output may worsen in systems having multiple cascaded stages, such as in a solid-state radar system with cascaded amplifiers. Accordingly, the performance loss accumulates.
Additionally, it is common that RF transistor-based circuits will tend to exhibit their own natural droop over the course of a powering cycle. For example, high (e.g., microwave) frequency RF transistor-based circuitry in a pulsed radar system will tend to exhibit a droop in gain that worsens over the course of the transmit pulse. This may be attributable to heating of the RF transistor junction during an RF pulse, which, in turn, may cause a decrease in the transistor output power during the RF transmit pulse. The RF output power is no longer constant throughout the RF pulse, resulting in suboptimal performance.
When a voltage regulator exhibiting its own droop is used with a transistor-based circuit having its own internal droop, the overall performance loss exacerbates. That is, the droop in the regulator output voltage causes a decrease in the RF transistor power output, thereby adding to an already decreasing output power that is caused by the characteristics of the RF transistor.
In summary, so-called xe2x80x9creal worldxe2x80x9d systems using voltage regulators with real world RF transistor-based load circuits tend to suffer significant performance losses associated with regulator voltage droop and/or internal RF transistor gain droop. In high stability systems, like solid state-pulsed radar systems, these performance losses can be a significant problem. This problem can be mitigated somewhat by using custom transistors (or by screening commercial-off-the-shelf [COTS] transistors), but this may greatly increase the costs of production. In many markets, such as for low- to medium-production military applications, these cost increases may not be acceptable.
Finally, it can be readily appreciated that the problem of voltage droop exists in other contexts. For example, instead of a transistor load, there may be some other component, device, or system, whose output response (e.g., voltage, gain, power, etc.) exhibits some undesirable variation over time. Also, the variation of this output response or gain may increase over some time period, decrease over some time period, or increase and decrease at points over a time period. The common problem is that of how to control (or compensate for) the time variable output response in order to render the desired output response. Generally, the desired output response is constant or flat over some period of time for the system at issue. Sometimes, a non-flat response may be desired.
Other problems and drawbacks also exist.
An embodiment of the present invention comprises a voltage regulator including a droop compensation circuit and an energy recovery circuit. The droop compensation circuit compensates for a regulator output voltage that is to be changed over a period of time. The regulator output voltage could be changed to compensate for regulator output voltage droop, load transistor droop, and/or any other output response that varies over time. The energy recovery circuit permits excess energy stored in the regulator output to be transferred from the regulator output to the input of the regulator. This transfer of energy may occur upon completion of a transmit gate during which the droop compensation circuit is operative.
The energy recovery circuit may include an active switch that is enabled in such a way that current can flow from an output capacitance of the voltage regulator to an input capacitance in the voltage regulator. According to an aspect of the invention, the switch is a switching transistor that is activated by drive pulses issued by a controller in the energy recovery circuit. These drive pulses may be issued over a fixed or variable time period. These drive pulses may be issued at a fixed or variable frequency rate.
The energy recovery circuit can accelerate the recovery time of the regulator voltage output back to a nominal value in order to prepare for the next transmit gate. The energy recovery circuit may improve the overall power efficiency of the voltage regulator, reduce heat generation, and improve reliability.
Accordingly, it is one object of the present invention to overcome one or more of the aforementioned and other limitations of existing systems and methods for regulating voltage supplied to an electronic circuit.
It is another object of the invention to provide a voltage regulator that solves or mitigates the problem of droop in electronic circuits in a manner that preserves power efficiency.
It is another object of the invention to provide a voltage regulator that solves or mitigates the problem of droop in electronic circuits in a manner that avoids excessive heat generation.
It is another object of the invention to provide a voltage regulator that solves or mitigates the problem of droop in electronic circuits in a manner that maintains good reliability.
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention. It will become apparent from the drawings and detailed description that other objects, advantages and benefits of the invention also exist.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the system and methods, particularly pointed out in the written description and claims hereof as well as the appended drawings.